The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for a chemical mechanical polishing apparatus.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A reoccurring problem in CMP is the so-called xe2x80x9cedge-effectxe2x80x9d, i.e., the tendency for the edge of the substrate to be polished at a different rate than the center of the substrate. The edge effect typically results in over-polishing (the removal of too much material from the substrate) of the substrate perimeter, e.g., the outermost five to ten millimeters of a 200 mm wafer. This over-polishing reduces the overall flatness of the substrate, makes the edge of the substrate unsuitable for integrated circuit fabrication, and decreases the process yield.
In view of the foregoing, there is a need for a CMP which provides the desired substrate surface flatness and finish while reducing or minimizing the edge effect.
In one aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head includes a base, a support structure movably connected to the base, and a flexible member connected to and extending beneath the support structure. A lower surface of the flexible member provides a substrate-receiving surface. A projection extends from the support structure to contact an upper surface of the flexible member at a location interior to an outer perimeter of the substrate-receiving surface.
Implementations of the invention may include the following. The carrier head may have a pressure mechanism, such as a bladder, for applying a downward force to the support structure. A retaining ring may be connected to the base and define a substrate-receiving recess. The contact area may be substantially contiguous with a region of a substrate which is potentially underpolished. The projection may contact the upper surface of the flexible member in a substantially annular contact area, or in a substantially circular contact area near the center of the substrate-receiving surface. The projection may be detachable from the support member. The lower surface of the support member may include one or more annular recesses, and the projection may comprise one or more O-rings fitted into the recesses. An outer edge of the support member may include a downwardly-projecting rim, the flexible member may extend around the outer edge of the support member, and the projection may be located interior to the rim.
In another aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus having a port in fluid communication with a chamber through which fluid is directed to generate a stream of fluid. The carrier head has a base and a flexible member connected to and extending beneath the base to define the chamber. A lower surface of the flexible member provides a substrate-receiving surface. The stream impinges upon an upper surface of the flexible member to create a localized area of increased pressure.
Implementations of the invention may include the following. The localized area of increased pressure may be substantially contiguous with a region of the substrate which is potentially underpolished, and may be located interior to an outer edge of the substrate-receiving surface. The fluid may be air. The carrier head may have a support structure having a passage extending therethrough, where one end of the passage is fluidly coupled to a pump and another end of the passage is fluidly coupled to the port.
In another aspect, the invention is directed to a carrier head having a base, a support structure, and a flexible member to define a chamber. A lower surface of the flexible member provides a substrate-receiving surface. The chamber is pressurizable to providing a first force to an upper surface of the flexible member. The carrier head also has means for applying a second, additional force to the upper surface of the flexible member in a localized contact area located interior to an outer edge of the substrate-receiving surface.
In another aspect, the invention is directed to a method of polishing a substrate. The method includes lacing a first face of the substrate against a substrate-receiving surface of a flexible member of a carrier head, the flexible member connected to and extending beneath a support structure of the carrier head to define a chamber, and positioning a second face of the substrate against a polishing pad. The chamber is pressurized to apply a first force to an upper surface of the flexible member, and a second, additional force is applied to the upper surface of the flexible member in a localized contact area.
Implementations of the invention may include the following. The localized contact area may be located interior to an outer edge of the substrate-receiving surface, and may be substantially contiguous with a region of the substrate which is potentially underpolished. The additional force may be applied by contacting the upper surface of the flexible member with a projection which extends from the support structure, or by contacting the upper surface of the flexible member with a fluid stream.
In another aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head includes a base, a support structure movably connected to the base, and a flexible member connected to and extending beneath the support structure. A lower surface of the flexible member provides a substrate-receiving surface. An annular seal is connected to the base and abuts an upper surface of the flexible member to define an inner chamber and an outer chamber around the inner chamber. The inner and outer chambers are pressurizable to force the annular seal against the flexible member to create a substantially fluid-tight seal between the inner chamber and the outer chamber.
Implementations of the invention may include the following. The carrier head may include a first pump fluidly coupled to the inner chamber and a second pump fluidly coupled to the outer chamber so that pressures in the chambers may be independently controlled. The annular seal may include a base portion contacting the flexible member and a stem portion clamped to the base. Advantages of the invention include the following. The edge effect is reduced, and the resulting flatness and finish of the substrate is substantially uniform.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.